Assuming we are playing in an environment in which most play a strong 1N, we have wrong-sided the contract. I have never understood any pair would open this sort of hand 1S in a strong 1N method....not only is one often wrong-siding the notrump, but opener has an horrendous rebid problem over a 1N response, especially in a 2/1 method. Of course, some pairs can solve this by a slow, tortured 2C, promising extras. Just kidding (well, no...not kidding, I have seen this)

As for the play, this is one of those hands where it is impossible, for me at any rate, to make up my mind as to how I will cater to all eventualities. I win a top heart, spurning the finesse, since losing the hook will leave me poorly placed if/when they switch to a diamond and EST does not have the 10.

I play spade to the Ace and then towards the jack.

I need to know what happens at that point

If the hook wins, I cash the King....if rho follows, then I have 5 spade tricks and I will stop playing spades immediately, since I don't want to make any more pitches from my hand than is necessary. I'd probably advance a low club towards my hand: it will be difficult for RHO to rise with the Queen if he lacks the Ace.

But the odds are that spades are not sitting that nicely...so I'd need to know what happened before committing to my line.

'one of the great markers of the advance of human kindness is the howls you will hear from the Men of God' Johann Hari

Assuming we are playing in an environment in which most play a strong 1N, we have wrong-sided the contract. I have never understood any pair would open this sort of hand 1S in a strong 1N method....not only is one often wrong-siding the notrump, but opener has an horrendous rebid problem over a 1N response, especially in a 2/1 method. Of course, some pairs can solve this by a slow, tortured 2C, promising extras. Just kidding (well, no...not kidding, I have seen this)

Oh, I definitely prefer to open 1N on such hands, but this was a pickup partnership. I also just moved back to France, so I don't actually know what percentage of the field would open 1N with a 5cM, but a non-educated guess would be somewhere between 30% and 70% (IOW, not everyone, but not no one) either.

I also started with high heart, spade to the ace, jack (holding) and king. Spades break 4=2.

I'd play the ♥J at trick one. If we don't have 5 spade tricks, we most likely need the heart finesse anyway, and we are short on entries for all the finesses we want to try (spade, heart, clubs). If we do have 5 spade tricks, I don't mind if they switch to a diamond after winning ♥Q as it means they help me explore one of the options for my 9th trick.

The egos of bridge players seem to be larger than that of the general population. Which is actually pretty strange, when one considers how humbling a game it is... Michael Rosenberg

The contract is poor.
Making this contract without clubs requires either 5 spades and 3 heart tricks, which is a 9% chance, or we need 7 tricks from the major and a second trick from diamonds. The latter is tricky because East can go in with a diamond honor from QT or KT once our spade entry is gone. Playing on spades first does not look good.

If the heart finesse works I see no urgency taking it on the opening lead. If the heart finesse fails there may be advantage not to take it since East will not be able to continue hearts.

Since we very likely need some club tricks I see two alternative line of play

1) Win the heart ace and come to the spade ace and run the club 9.
If the queen of clubs is with West we have at least 2 club tricks , 2 heart tricks at least one diamond trick and hopefully enough time to establish spades for 4 tricks in time. If we get 4 tricks in the minors we need only one of the major suit finesses to work.
We are not home, but our chances look better than establishing spades first.

2) Win heart ace and play king of clubs. Defenders often duck this assuming you have the queen too for such a play. If the club king looses to East,East will probably switch to diamonds and you can insert the 9.
If West wins and continues hearts your percentage play is to take the heart finesse and continue establishing 2 club tricks.

Not sure which line is better, but both look better to me than playing on spades immediately. It probably depends which black finesse is working. line 1 may be slightly better.

Even if spades behave, I'm not sure what to discard on the third spade. And I probably need to establish some club tricks, although I don't have the entries to both pick up ♣Qxx with West and score the fourth club. But if I try the J at trick one and RHO shifts to a diamond, that might ruin everything. So I'm tempted to win the first trick and play a club towards the nine.

If it loses to the Qxx, the play won't necessarily cost a trick, and it might actually win a trick if RHO plays low from Qx.
Also, it might give LHO a problem or two. For instance, if he thinks I've played the nine from QJ9(x...), is it necessarily a good idea to win with the ace from ♣Axx(x...)? And then,

* if he ducks, what should he do when I lead another club towards dummy?
* if he wins, is it is necessarily clear whether to continue hearts or shift to a diamond, or maybe a spade?

So here's a rudimentary plan:

1) Win the first trick with A or K, partly to avoid an unpleasant diamond shift.
2) Play a club towards the nine, with the idea of
* not squeezing myself (easier on a third round of spades);
* establishing club tricks;
* letting LHO err instead of me (or if the trick two play by me is a mistake, allowing LHO to make up for it);
3) Play normal bridge from then on. (E.g. by taking the finesse if LHO wins and continues hearts.)

Thanks for the input.
At the table, I won the ace, played three rounds of spades and let lefty win the fourth, pitching a diamond and a club. Then came heart to the jack and queen, and another heart. At that point I tried to sneak a club through, but righty went up with the queen after some thought. As the diamond ten was offside (so nothing was going to work legitimately), the roof fell in and I ended up down three.